A. Field of the Invention
The present invention relates generally to digital signal transmission and reception, and more particularly, to a system and method for simultaneously authorizing a plurality of virtual channels of multiplexed digital services, including imaging services.
B. Description of the Relevant Art
With the growing trend toward a merger of the previously separate technologies of telecommunications including voice and data telecommunications and television including satellite, broadcast and cable television, there has emerged an increased interest in developing adaptable transmission systems capable of handling a collection of such services. The primary media investigated for providing such services to date comprise, for example, coaxial cable, land-based microwave, so-called cellular radio, broadcast FM, broadcast satellite and optical fiber, to name a few.
Multi-service communications systems may transmit different services over one or more different frequency channels. Each frequency channel may carry more than one service. Therefore, to gain access to a particular service, a receiver must have information to enable it to tune to the frequency channel carrying the desired service and then to select the desired service from the several services provided on that frequency channel. Such information concerning the details of access to a selected service is not pertinent to the subscriber.
U.S. Pat. No. 4,908,859 to Bennett, entitled "Receiver Access Interface to Service Components in Television Channel" discloses a receiver interface system that stores a service definition table, a service-to-channel map, and a channel configuration map. The service definition table defines the relation between service components and service numbers. The service-to-channel map defines the relationship between service numbers and interface channel numbers. The channel configuration may defines the relationship between frequency channels and interface channel numbers. Using these relationships, a receiver can locate and access a service selected by a user in signals transmitted over various frequency channels.
U.S. Pat. No. 5,200,823 to Yoneda et al., entitled "Virtual Channels for a Multiplexed Analog Component (MAC) Television System", contains a description of a television system for providing services, including video, audio, and text services, to remotely located subscribers over a plurality of channels. A decoder at the subscriber location receives audio, video, and text components over each physical channel. The decoder contains a mapping of each physical channel to virtual channel numbers. Each virtual channel may use a different combination of components. For example, one virtual channel may comprise linked pages of text service. A user can select a virtual channel using a selector and thereby receive the combination of service components defined by the virtual channel.
FIGS. 5A and 5B illustrate the operation of a MAC implementation. By way of example, access to the following three services is desired: radio service #1 (RS#1), teletext service #2 (TTX#2), and data service (DS#3). The three services are packaged together to form virtual channel number 1 (VC#1). FIG. 5A provides a pictorial representation of virtual channel number 1. As can be seen, because virtual channel number 1 does not include a video service, the first box is blacked out in this pictorial representation. Information containing the definition for virtual channel number 1 is sent to the decoder every session, a basic unit of timing for the decoder as discussed below. Thus, in each session, the decoder is authorized for the three services defined in virtual channel number 1. FIG. 5B illustrates that virtual channel 1 is authorized by the decoder over eight sessions.
U.S. application Ser. No. 08/027,782, entitled "Apparatus Providing Dynamic Virtual Service Selection in a Multi-Service Communication System," filed Mar. 8, 1993, now U.S. Pat. No. 5,359,601, discloses inter alia a receiver system whereby a plurality of different services may, on a time-varying basis, define a virtual channel. Thus, the virtual channel number may correspond to a first service in a first time period and a second service during a second time period. Accordingly, the system operator may design dynamic virtual service selections from a plurality of basic services. By way of example, the operator may define a "Cowboy Channel" that a subscriber may select using a virtual channel number. By tuning to the virtual channel number, the subscriber may view a cowboy documentary from basic service number 1 between 5:00 PM and 7:00 PM, a cowboy movie from basic service number 30 between 7:00 PM and 9:00 PM, and a western television series from basic service number 3 from 9:00 PM to 11:30 PM.
In the foregoing systems, a single service is typically defined for each virtual channel. Therefore, a problem arises when a subscriber wants to simultaneously view or access more than one service. For example, a subscriber may wish to view a television service and at the same time access a data service, or read from a teletext service while listening to a radio service. The systems described above only access or authorize one virtual channel at a given time. The aforementioned problem cannot be solved simply by packaging two services together in one virtual channel because some subscribers may not wish to access both services and thus will be unwilling to pay for the extra service.
One solution to the problem of providing simultaneous access to a plurality of services is to define additional virtual channels for each possible combination of services. By selecting the appropriate virtual channel, the subscriber can access the desired combination of services. If another subscriber does not want a particular service, that subscriber will not be authorized to receive it. However, this solution is problematic because only a finite number of virtual channels are available. As the number of available services increases, the number of combinations of services rapidly increases thereby exceeding the number of available virtual channels. Limited by the number of virtual channels available, the operator may be required to reduce the number of individual services provided. This results in fewer choices for the subscriber and reduced flexibility. Thus, defining virtual channels in this manner is wasteful, particularly if channels can be used for other services.